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Comparison of the ability of mouse hepatocytes and mouse-liver S9 to activate nitrosamines and other carcinogens to mutagenic factors for Salmonella TA1535
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tion of the fungus was obtained. So concentrations of 300, 400, 500 and 600/~g/ml induced 370, 630, 1030 and 1760 segregants per 100 colonies respectively. By analysing genetically the colour segregants, it was shown that most of them were derived by mitotic crossing-over, whereas the non-disjunctional segregants were at a rather low level. In the case of indole-3-butyric acid the metabolic activation technique was also used and it was shown that when $9 was added to the chemical a 2-3-fold further increase of the number of segregants was obtained.
75 Kerklaan, P., S. Bouter and G. Mohn, Department of Radiation Genetics and Chemical Mutagenesis, University of Leiden (The Netherlands) Comparison of the ability of mouse hepatocytes and mouse-liver S9 to activate nitrosamines and other carcinogens to mutagenic factors for Salmonella TA1535
In previous experiments it was shown that rodent-liver $9 homogenates have substantially lower capacity for activating carcinogenic nitrosamines to mutagens than expected from the mutagenic activity of the same compounds in intrasanguineous host-mediated assays. To assay whether homogenization of liver cells during preparation of $9 results in a reduction of bioactivating properties, hepatocytes from Swiss albino mice were isolated as suspensions of single cells and their biological activity was determined. Mutagen activation kinetics and cell-density dependence for mutation induction were measured with cyclophosphamide and nitrosodimethylamine and optimal conditions for mutagenesis were determined. Under standardized incubation conditions, CP, NDMA and other carcinogens such as nitrosomethylethylamineand 1,2-dimethylhydrazinewere mutagenic towards TA1535 in the presence of hepatocytes. Under those conditions, $9 prepared from the same mouse strain was a less efficient metabolizing system. Nitrosodiethylamine appears not to be significantly activated with any of the two in vitro systems. These results, though preliminary, indicate that freshly isolated hepatocytes have greater capacity to activate precarcinogens such as nitrosamines than $9 preparations do and are, therefore, probably beter representatives of the in vivo metabolic activity of the liver. The non-mutagenicity of NDEA, however, also indicates that improvements and further comparative studies are necessary to better appreciate the usefulness of hepatocytes as alternative for $9 preparations in routine testing procedures. Research sponsored by a grant of the Koningin Wilhelmina Fonds of The Netherlands.
76 Khera, A.K., D.G. Wibberley, Department of Pharmacy, University of Aston, Birmingham B4 7ET (Great Britain)
tion of the fungus was obtained. So concentrations of 300, 400, 500 and 600/~g/ml induced 370, 630, 1030 and 1760 segregants per 100 colonies respectively. By analysing genetically the colour segregants, it was shown that most of them were derived by mitotic crossing-over, whereas the non-disjunctional segregants were at a rather low level. In the case of indole-3-butyric acid the metabolic activation technique was also used and it was shown that when $9 was added to the chemical a 2-3-fold further increase of the number of segregants was obtained.
75 Kerklaan, P., S. Bouter and G. Mohn, Department of Radiation Genetics and Chemical Mutagenesis, University of Leiden (The Netherlands) Comparison of the ability of mouse hepatocytes and mouse-liver S9 to activate nitrosamines and other carcinogens to mutagenic factors for Salmonella TA1535
In previous experiments it was shown that rodent-liver $9 homogenates have substantially lower capacity for activating carcinogenic nitrosamines to mutagens than expected from the mutagenic activity of the same compounds in intrasanguineous host-mediated assays. To assay whether homogenization of liver cells during preparation of $9 results in a reduction of bioactivating properties, hepatocytes from Swiss albino mice were isolated as suspensions of single cells and their biological activity was determined. Mutagen activation kinetics and cell-density dependence for mutation induction were measured with cyclophosphamide and nitrosodimethylamine and optimal conditions for mutagenesis were determined. Under standardized incubation conditions, CP, NDMA and other carcinogens such as nitrosomethylethylamineand 1,2-dimethylhydrazinewere mutagenic towards TA1535 in the presence of hepatocytes. Under those conditions, $9 prepared from the same mouse strain was a less efficient metabolizing system. Nitrosodiethylamine appears not to be significantly activated with any of the two in vitro systems. These results, though preliminary, indicate that freshly isolated hepatocytes have greater capacity to activate precarcinogens such as nitrosamines than $9 preparations do and are, therefore, probably beter representatives of the in vivo metabolic activity of the liver. The non-mutagenicity of NDEA, however, also indicates that improvements and further comparative studies are necessary to better appreciate the usefulness of hepatocytes as alternative for $9 preparations in routine testing procedures. Research sponsored by a grant of the Koningin Wilhelmina Fonds of The Netherlands.
76 Khera, A.K., D.G. Wibberley, Department of Pharmacy, University of Aston, Birmingham B4 7ET (Great Britain)